Serial infection with two different dengue virus serotypes has been proposed as the mechanism of the dengue hemorrhagic fever/shock syndrome (DHF/SS) seen in the Pacific. A second dengue infection in the face of low levels of antibody is thought to generate a host damaging immune response. Heterotypic immunity is not long lasting, despite the persistence of circulating antibody. In infants with maternal dengue antibody, a first dengue infection theoretically may have a similar serious effect. DHF/SS is unknown in the Caribbean, although our previous studies indicate two dengue virus sero types, 2 and 3, coexist here. A prospective actuarial study of the effects of dengue virus infection in infants with or without maternal dengue antibody, is planned in Santo Domingo, Dominican Republic, where our previous investigations indicate dengue is endemic. We seek to determine the morbidity and mortality of infants who experience dengue infection. The question being asked is whether maternal dengue antibody prejudices the health of infants who are exposed to dengue infection by 4 or 8 months. 4000 infants will be followed over 2 years. Based on our previous studies it is anticipated that approximately 3000 infants will be born with dengue antibody, and around 10% will be infected with dengue virus every 4 months. The occurrence of stillbirths and specific congenital abnormalities in infants born to women with high, low or no titers of dengue antibody will also be compared, to seek a possible fetal effect of maternal dengue infection during pregnancy. If dengue infection is having damaging effects on maternal or child health, then its widespread involvement in certain urban populations and the lack of effective control measures presently in force, make dengue a community health hazard of great importance. Dengue epidemics have been increasing in frequency in the past decade and could recur in receptive areas of the United States where Aedes aegypti exist.